There is considerable interest in developing sensors that act as analogs of the mammalian olfactory system (Lundstrom et al. (1991) Nature 352:47-50; Shurmer and Gardner (1992) Sens. Act. B 8:1-11). This system is thought to utilize probabilistic repertoires of many different receptors to recognize a single odorant (Reed (1992) Neuron 8:205-209; Lancet and Ben-Airie (1993) Curr. Biol. 3:668-674). In such a configuration, the burden of recognition is not on highly specific receptors, as in the traditional "lock-and-key" molecular recognition approach to chemical sensing, but lies instead on the distributed pattern processing of the olfactory bulb and the brain (Kauer (1991) TINS 14:79-85; DeVries and Baylor (1993) Cell 10(S):139-149). Prior attempts to produce a broadly responsive sensor array have exploited heated metal oxide thin film resistors (Gardner et al. (1991) Sens. Act. B 4:117-121; Gardner et al. (1991) Sens. Act. B 6:71-75; Corcoran et al. (1993) Sens. Act. B 15:32-37), polymer sorption layers on the surfaces of acoustic wave resonators (Grate and Abraham (1991) Sens. Act. B 3:85-111; Grate et al. (1993) Anal. Chem. 65:1868-1881), arrays of electrochemical detectors (Stetter et al. (1986) Anal. Chem. 58:860-866; Stetter et al. (1990) Sens. Act. B 1:43-47; Stetter et al. (1993) Anal. Chem. Acta 284:1-11), or conductive polymers (Pearce et al. (1993) Analyst 118:371-377; Shurmer et al. (1991) Sens. Act. B 4:29-33). Arrays of metal oxide thin film resistors, typically based on SnO.sub.2 films that have been coated with various catalysts, yield distinct, diagnostic responses for several vapors (Gardner et al (1991) Sens. Act. B 4:117-121; Gardner et al. (1991) Sens. Act. B 6:71-75; Corcoran et al. (1993) Sens. Act. B 15:32-37). However, due to the lack of understanding of catalyst function, SnO.sub.2 arrays do not allow deliberate chemical control of the response of elements in the arrays nor reproducibility of response from array to array. Surface acoustic wave resonators are extremely sensitive to both mass and acoustic impedance changes of the coatings in array elements, but the signal transduction mechanism involves somewhat complicated electronics, requiring frequency measurement to 1 Hz while sustaining a 100 MHz Rayleigh wave in the crystal (Grate and Abraham (1991) Sens. Act. B 3:85-111; Grate et al. (1993) Anal. Chem. 65:1868-1881). Attempts have been made to construct sensors with conducting polymer elements that have been grown electrochemically through nominally identical polymer films and coatings (Pearce et al. (1993) Analyst 118:371-377; Shurmer et al. (1991) Sens. Act. B 4:29-33; Topart and Josowicz (1992) J. Phys. Chem. 96:7824-7830; Charlesworth et al. (1993) J. Phys. Chem. 97:5418-5423).
It is an object herein to provide a broadly responsive analyte detection sensor based on one or more "chemiresistor" elements. Such elements are simply prepared and are readily modified chemically to respond to a broad range of analytes. Such elements may also respond to temperature and current variation. In addition, these sensors yield a rapid, low power, dc electrical signal in response to the fluid of interest, and their signals are readily integrated with software or hardware-based neural networks for purposes of analyte identification.